1. Technical Field of the Invention
The present invention relates to a tail structure of a shield driving machine, and in particular relates to an improvement technique of the tail sealing portion of this type of shield driving machine.
2. Description of Prior Arts
In a shield construction applied to building of a subway tunnel in a city zone, recently, reduction of the construction costs and shortening of the construction term are of importance. In order to meet these requests, it is attempted that the excavation distance per shield driving machine is lengthened.
Furthermore, in shaft building work in a shield construction, since it becomes very difficult to secure a site in line with recent overcrowding of a city zone, and the installation level of a shield tunnel is even deepening, the costs and term required for building a shaft has been increased, wherein lengthening of the excavation distance of a shield driving machine is further accelerated.
Although various problems arise in line with a lengthening of the excavation distance of a shield driving machine, the durability of the tail seal portion of a shield driving machine is an important theme. The tail seal portion which prevents peripheral water, earth and sand, and back-filling materials from flowing into the shield driving machine body is usually constructed as shown in FIG. 13.
The tail seal portion "a" illustrated in the drawing prevented peripheral water, etc., from flowing into the machine body by providing a plurality of flutes of tail brush "d", which is slidably brought into contact with the outer circumferential surface of segments "c", on the inner circumferential surface of a skin plate "b" at the tail side, and by filling a semi-solid filling material "e" such as grease between the tail brushes "d".
However, with such a conventional structure of the tail seal portion "a", especially, in line with a lengthening of the excavation distance of a shield driving machine, there were technical problems as described below;
That is, at the tail seal portion "a" illustrated in FIG. 13, since the tail brushes "d" are brought into contact with segments "c" while the shield driving machine is excavating, they slidably move in line with the excavation. Therefore, the tail brushes "d" are worn by frictions with the segments "c", whereby peripheral water invades the tail portion of the shield driving machine while driving a long distance.
Furthermore, a back-filling material invades the tail brushes "d" and is adhered thereto gradually, wherein the adhered back-filling material is solidified. The resiliency of the tail brushes "d" is gradually spoiled, and it becomes difficult to follow a change of the clearance between the skin plate "b" and segments "c", wherein when driving and excavating a long distance, peripheral water, etc., invades the tail portion of the shield driving machine.
However, construction of tunnels by a shield driving machine is not limited to construction of tunnels for subways and roads for transport facilities. For example, the inventors disclosed utilization of the present invention in construction of water-intake tunnels to intake sea water for a plant producing fresh water by using sea water in Japanese Patent Application No. 218492 of 1997.
That is, in order to secure drinking water on islands where it scarcely rains or in desert areas, a plant producing fresh water is installed in the vicinity of a sea shore. Furthermore, sea water is prime water for treatment in salt production plants, wherein in these types of sea water treatment facilities, it is necessary to introduce sea water into a plant producing fresh water.
Therefore, in such a sea water treatment facility, conventionally, sea water was introduced through a water-intake tunnel in which vinyl chloride tube covered with unwoven cloth, having a number of penetrated water-intake pores formed thereon, and porous Hume pipes are laid, However, since a water-intake tunnel of such construction is buried by an excavation construction method or a sinking and laying method, the site on the ground right above the laying position and/or its surrounding are exclusively occupied for the sinking and laying work. Therefore, from this viewpoint, there are various limitations in the construction work resulting therefrom.
Therefore, the inventors developed a technique for building these types of water-intake tunnels by a shield driving method. Segments used to build such water-intake tunnels are, as shown in FIG. 14, such that a permeable member 2 is attached to the outside of a body plate 1 such as steel segments and ductile segments conventionally used for a usual shield construction method.
The permeable member 2 is made of porous concrete, etc., and is so constructed that underground water passing through the permeable member 2 is positively taken into the inside through water-intake openings (not illustrated) which are openable and closable, and secured at the body plate 1.
However, when building a water-intake tunnel by a shield driving machine, using such water-intake segments 3, particularly, there were such technical problems as described below as regards the tail portion of a shield driving machine.
That is, as described above, the tail structure of a shield driving machine used for a usual shield construction method, plural flutes of tail brushes "d" which are slidably brought into contact with the outer circumferential surface of segments "c" were disposed on the inner circumferential surface of the skin plate "b" at the tail side, and a filling material "e" was filled in between the tail brushes "d", wherein peripheral water was prevented from invading inside.
However, if the tail structure of such a construction is applied to the abovementioned water-intake segments 3, it is impossible to cover the entirety of the permeable member 2 even in a case where, as shown in FIG. 14, the tail brushes "d" are slidably brought into contact with the outer circumferential surface of the water-intake segments 3. Therefore, peripheral water invades in a channel indicated by the arrow depicted by a solid line, and the tail structure does not function as a tail seal.
Furthermore, if a filling material "e" is filled in between the tail brushes "d" even though the entirety of the permeable portion 2 can be covered by the tail brushes "d", grease clogs pores of the permeable member 2 and reduces the permeability of the permeable member 2. Therefore, the filling material "e" can not be used. Unless the filling material "e" is used, peripheral water invades through the clearance of the tail brushes "d", wherein the tail brushes "d" can not function as a tale seal.